Ductile chromium



3,074,153 DUCTILE COMIUM Stanley J. Paprocki and George W. Cunningham, Colum bus, Ghio, assignors to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Filed May 17, 1961, Ser. No. 110,829

4 Claims. (Cl. 29-1825) The invention relates to a novel ductile chromium composition, and to a method for producing the same. Pure chromium and alloys high in chromium are notoriously difiicult to work. In particular, chromium and chromium base alloys lack the property of ductility, which renders them unsuitable for drawing into rods, wire, tubes and the like, or other similar operations. Due to other outstanding properties of the metal such as resistance to corrosion, it would be desirable to fabricate it into the shapes mentioned, if only some method of improving its ductility could be found.

It is, accordingly, the object of the invention to provide a chromium composition with greater ductility than is presently known.

It is a further object to provide a method for making a composition of the kind described.

Both the foregoing objects are attained by my discovery that the ductility of chromium and alloys high in chromium can be increased by adding a comparatively small amount of uranium nitride, preferably by powder metallurgy methods.

As little as about one weight percent (1 w/o) uranium nitride added to chromium or any of its alloys brings about an enhanced ductility, and, equally, if not even more surprising, as high as 40 w/o uranium nitride produces the same effect. Ordinarily it would be expected that the addition of a ceramic substance such as uranium nitride to a metal would increase its brittleness, but the opposite takes place in this instance. Several speculative explanations of this phenomenon have been offered, but as none have been conclusively proved, it would serve no purpose to set them forth at present. My invention is offered on the basis of empirical findings made as the result of actual experiments.

The amount of uranium nitride added to the chromium or chromium alloy does not appear to be critical, as is already indicated by the fact that even a composition of 40 w/o uranium nitride has improved ductility. However, there is doubtless an upper limit beyond which further additions give no benefit, since as the ceramic uranium nitride becomes preponderant over the metal, the ordinary brittleness of ceramics necessarily takes over for purely physical reasons. Likewise, at the lower end, there is doubtless a point where the uranium nitride is present in such minute amounts that the effect on the metal becomes negligible. However, over a very wide range, it is apparent that the addition of uranium nitride does produce a marked increase in ductility.

No particular method is necessary for incorporating the uranium nitride (UN) into the metal, and any of the known techniques in the field may be used. However, I prefer the method of powder metallurgy, i.e. of compressing UN and the metal in powder form and then sintering them together. The powder particle size, pres- 3,674,153- Patented Jan. 22, 1.963

sure, and temperature do not appear to be critical, but I prefer 235 mesh powders compressed at 50 tons per square inch with an organic binder, which are then sintered at about 2300 F. for about two hours.

Example I Annealed electrolytic chromium powder of 235 mesh size was mixed with uranium nitride powder of the same size so as to make the weight percentage of UN twenty. The two powders were blended together dry in a U-type mixer for one hour.

A /2 w/o binder, a saturated camphor-in-methanol solution, was added and the powders were blended together an additional hour.

The blended powders were then compressed into compacts 60 mils thick under a pressure of 50 tons per square inch. They were then sintered for two hours in a furnace with an inert atmosphere at 2300 P.

On cooling, the compacts presented a firm, smooth appearance and could be bent around a fifty cent piece without cracking.

Example II The same technique was followed as set forth in Example I except that the UN was 40 w/o in the compacts.

The 60 mil compacts could be bent around a fifty cent piece without cracking.

Example 111 The same technique was followed as in Example 1 except that the blended powders were 100 mesh.

The 60 mil compacts could be bent around a fifty cent piece without cracking.

Example IV The same technique was followed as in Example I except that the sintering temperature was 2000 F.

The 60 mil compacts could be bent around a fifty cent piece without cracking.

Example V The same technique was followed as in Example I except that the sintering temperature was '2750 The 60 mil compacts could be bent around a fifty cent piece without cracking.

It will be understood that this invention is not to be limited to the details given herein, but that it may be modified within the scope of the appended claims.

What is claimed is:

1. A ductile sintered powder composition consisting essentially of chromium and from about one to forty weight percent uranium nitride.

'2. A ductile sintered powder composition consisting essentially of twenty weight percent uranium nitride and the balance chromium.

3. A method of making ductile chromium comprising admixing at least one weight percent uranium nitride powder to a powder comprising chromium, pressing the mixed powders into shape, and sintering them at a temperature within the range of 2000 to 2750 F.

4. The method of claim 3 where the elevated temperature is 2300 F.

No references cited. 

1. A DUCTILE SINTERED POWDER COMPOSITION CONSISTING ESSENTIALLY OF CHROMIUM AND FROM ABOUT ONE TO FORTY WEIGHT PERCENT URANIUM NITRIDE. 